Synthesis of oligonucleotide arrays using photocleavable protecting groups

ABSTRACT

Novel compounds are provided which are useful as linking groups in chemical synthesis, preferably in the solid phase synthesis of oligonucleotides and polypeptides. These compounds are generally photolabile and comprise protecting groups which can be removed by photolysis to unmask a reactive group. The protecting group has the general formula Ar--C(R 1 )(R 2 )--O--C(O)-- wherein: 
     Ar is an optionally substituted fused polycyclic aryl or heteroaromatic group or a vinylogous derivative thereof; 
     R 1  and R2 are independently H, optionally substituted alkyl, alkenyl or alkynyl, optionally substituted aryl or optionally substituted heteroaromatic, or a vinylogous derivative of the foregoing; and 
     X is a leaving group, a chemical fragment linked to Ar--C(R 1 )(R 2 )--O--C(O)-- via a heteroatom, or a solid support; provided that when Ar is 1-pyrenyl and R 1  =R 2  =H, X is not linked to Ar--C(R 1 )(R 2 )--O--C(O)-- via a nitrogen atom. Preferred embodiments are those in which Ar is a fused polycyclic aromatic hydrocarbon and in which the substituents on Ar, R 1  and R 2  are electron donating groups. A particularly preferred protecting group is the &#34;PYMOC&#34; protecting group, pyrenylmethyloxycarbonyl, where Ar=pyrenyl and R 1  =R 2  =H. 
     Also provided is a method of forming, from component molecules, a plurality of compounds on a support, each compound occupying a separate predefined region of the support, using the protected compounds described above.

The present invention was made with U.S. Government support under ATP Grant No. 70NANB5H1031, and the government may have certain rights in the invention.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a regular application claiming priority from Provisional U.S. Application Ser. No. 60,008,684, filed Dec. 15, 1995.

BACKGROUND OF THE INVENTION

The present invention relates to the area of chemical synthesis. More particularly, this invention relates to photolabile compounds, reagents for preparing the same and methods for their use as photocleavable linkers and protecting groups, particularly in the synthesis of high density molecular arrays on solid supports.

The use of a photolabile molecule as a linker to couple molecules to solid supports and to facilitate the subsequent cleavage reaction has received considerable attention during the last two decades. Photolysis offers a mild method of cleavage which complements traditional acidic or basic cleavage techniques. See, e.g., Lloyd-Williams et al. (1993) Tetrahedron 49:11065-11133. The rapidly growing field of combinatorial organic synthesis (see, e.g., Gallop et al. (1994) J. Med. Chem. 37:1233-1251; and Gordon et al. (1994) J. Med. Chem. 37:1385-1401) involving libraries of peptides and small molecules has markedly renewed interest in the use of photolabile linkers for the release of both ligands and tagging molecules.

A variety of ortho-benzyl compounds as photolabile protecting groups have been used in the course of optimizing the photolithographic synthesis of both peptides (see Fodor et al. (1994) Science 251:767-773) and oligonucleotides (see Pease et al. Proc. Natl. Acad. Sci. USA 91:5022-5026). See PCT patent publication Nos. WO 90/15070, WO 92/10092, and WO 94/10128; see also U.S. patent application Ser. No. 07/971,181, filed Nov. 2, 1992, (now abandoned) and Ser. No. 08/310,510, filed Sep. 22, 1994 (now abandoned); Holmes et al. (1994) in Peptides: Chemistry, Structure and Biology (Proceedings of the 13th American Peptide Symposium); Hodges et al. Eds.; ESCOM: Leiden; pp. 110-12, each of these references is incorporated herein by reference for all purposes. Examples of these compounds included the 6-nitroveratryl derived protecting groups, which incorporate two additional alkoxy groups into the benzene ring. Introduction of an a-methyl onto the benzylic carbon facilitated the photolytic cleavage with >350 nm UV light and resulted in the formation of a nitroso-ketone.

Photocleavable protecting groups and linkers should be stable to a variety of reagents (e.g., piperidine, TFA, and the like); be rapidly cleaved under mild conditions; and not generate highly reactive byproducts. The present invention provides such protecting groups and methods for their use in synthesizing high density molecular arrays.

SUMMARY OF THE INVENTION

According to a first aspect of the invention, novel compounds are provided which are useful as linking groups in chemical synthesis, preferably in the solid phase synthesis of oligonucleotides and polypeptides. These compounds are generally photolabile and comprise protecting groups which can be removed by photolysis to unmask a reactive group. The protecting group has the general formula Ar--C(R₁)(R₂)--O--C(O)-- wherein:

Ar is an optionally substituted fused polycyclic aryl or heteroaromatic group or a vinylogous derivative thereof;

R₁ and R₂ are independently H, optionally substituted alkyl, alkenyl or alkynyl, optionally substituted aryl or optionally substituted heteroaromatic, or a vinylogous derivative of the foregoing; and

X is a leaving group, a chemical fragment linked to Ar--C(R₁)(R₂)--O--C(O)-- via a heteroatom, or a solid support; provided that when Ar is 1-pyrenyl and R₁ =R₂ =H, X is not linked to Ar--C(R₁)(R₂)--O--C(O)-- via a nitrogen atom. Preferred embodiments are those in which Ar is a fused polycyclic aromatic hydrocarbon and in which the substituents on Ar, R₁ and R₂ are electron donating groups. Particularly preferred protecting groups are the "PYMOC" protecting group, pyrenylmethyloxycarbonyl, where Ar=1-pyrenyl and R₁ =R₂ =H, and the "ANMOC" protecting group, anthracenylmethyloxycarbonyl, where Ar=anthracenyl and R₁ =R₂ =H. Methods are provided for preparing these compounds.

This invention also provides reagents of the molecular formula Ar--C(R₁)(R₂)--O--C(O)--X, where Ar, R₁, and R₂ have the meanings ascribed above, for incorporating the protecting group into the molecule desired to be protected.

Another aspect of this invention provides a method of attaching a molecule with a reactive site to a support comprising the steps of:

(a) providing a support with a reactive site;

(b) binding a molecule to the reactive site, the molecule comprising a masked reactive site attached to a photolabile protecting group of the formula Ar--C(R₁)(R₂)--O--C(O)-- ,wherein:

Ar is an optionally substituted fused polycyclic aryl or heteroaromatic group or a vinylogously substituted derivative of the foregoing;

R₁ and R₂ are independently H, optionally substituted alkyl, alkenyl or alkynyl, or optionally substituted aryl or heteroaromatic group or a vinylogously substituted derivative of the foregoing;

to produce a derivatized support having immobilized thereon the molecule attached to the photolabile protecting group; and

(c) removing the photolabile protecting group to provide a derivatized support comprising the molecule with an unmasked reactive site immobilized thereon.

A related aspect of this invention provides a method of forming, from component molecules, a plurality of compounds on a support, each compound occupying a separate predefined region of the support, said method comprising the steps of:

(a) activating a region of the support;

(b) binding a molecule to the region, said molecule comprising a masked reactive site linked to a photolabile protecting group of the formula Ar--C(R₁)(R₂)--O--C(O)--, wherein:

Ar is an optionally substituted fused polycyclic aryl or heteroaromatic group or a vinylogously substituted derivative of the foregoing;

R₁ and R₂ are independently H, optionally substituted alkyl, alkenyl or alkynyl, or optionally substituted aryl or heteroaromatic group or a vinylogously substituted derivative of the foregoing;

(c) repeating steps (a) and (b) on other regions of the support whereby each of said other regions has bound thereto another molecule comprising a masked reactive site linked to the photolabile protecting group, wherein said another molecule may be the same or different from that used in step (b);

(d) removing the photolabile protecting group from one of the molecules bound to one of the regions of the support to provide a region bearing a molecule with an unmasked reactive site;

(e) binding an additional molecule to the molecule with an unmasked reactive site;

(f) repeating steps (d) and (e) on regions of the support until a desired plurality of compounds is formed from the component molecules, each compound occupying separate regions of the support.

This method finds particular utility in synthesizing high density arrays of nucleic acids on solid supports.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 and 2 show syntheses of 5'--O--pyrenylmethyloxycarbonyl ("PYMOC") protected deoxynucleoside 3'--O--cyanoethylphosphoramidites in a suitable form for coupling to a support.

FIG. 3 shows representative Ar groups that can be present in the compounds of this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The following definitions are set forth to illustrate and define the meaning and scope of the various terms used to describe the invention herein.

The term "alkyl" refers to a branched or straight chain acyclic, monovalent saturated hydrocarbon radical of one to twenty carbon atoms.

The term "alkenyl" refers to an unsaturated hydrocarbon radical which contains at least one carbon--carbon double bond and includes straight chain, branched chain and cyclic radicals.

The term "alkynyl" refers to an unsaturated hydrocarbon radical which contains at least one carbon--carbon triple bond and includes straight chain, branched chain and cyclic radicals.

The term "aryl" refers to an aromatic monovalent carbocyclic radical having a single ring (e.g., phenyl) or two condensed rings (e.g., naphthyl), which can optionally be mono-, di-, or tri-substituted, independently, with alkyl, lower-alkyl, cycloalkyl, hydroxylower-alkyl, aminolower-alkyl, hydroxyl, thiol, amino, halo, nitro, lower-alkylthio, lower-alkoxy, mono-lower-alkylamino, di-lower-alkylamino, acyl, hydroxycarbonyl, lower-alkoxycarbonyl, hydroxysulfonyl, lower-alkoxysulfonyl, lower-alkylsulfonyl, lower-alkylsulfinyl, trifluoromethyl, cyano, tetrazoyl, carbamoyl, lower-alkylcarbamoyl, and di-lower-alkylcarbamoyl. Alternatively, two adjacent positions of the aromatic ring may be substituted with a methylenedioxy or ethylenedioxy group. Typically, electron-donating substituents are preferred.

The term "heteroaromatic" refers to an aromatic monovalent mono- or poly-cyclic radical having at least one heteroatom within the ring, e.g., nitrogen, oxygen or sulfur, wherein the aromatic ring can optionally be mono-, di- or tri-substituted, independently, with alkyl, lower-alkyl, cycloalkyl, hydroxylower-alkyl, aminolower-alkyl, hydroxyl, thiol, amino, halo, nitro, lower-alkylthio, lower-alkoxy, mono-lower-alkylamino, di-lower-alkylamino, acyl, hydroxycarbonyl, lower-alkoxycarbonyl, hydroxysulfonyl, lower-alkoxysulfonyl, lower-alkylsulfonyl, lower-alkylsulfinyl, trifluoromethyl, cyano, tetrazoyl, carbamoyl, lower-alkylcarbamoyl, and di-lower-alkylcarbamoyl. For example, typical heteroaryl groups with one or more nitrogen atoms are tetrazoyl, pyridyl (e.g., 4-pyridyl, 3-pyridyl, 2-pyridyl), pyrrolyl (e.g., 2-pyrrolyl, 2-(N-alkyl)pyrrolyl), pyridazinyl, quinolyl (e.g. 2-quinolyl, 3-quinolyl etc.), imidazolyl, isoquinolyl, pyrazolyl, pyrazinyl, pyrimidinyl, pyridonyl or pyridazinonyl; typical oxygen heteroaryl radicals with an oxygen atom are 2-furyl, 3-furyl or benzofuranyl; typical sulfur heteroaryl radicals are thienyl, and benzothienyl; typical mixed heteroatom heteroaryl radicals are furazanyl and phenothiazinyl. Further the term also includes instances where a heteroatom within the ring has been oxidized, such as, for example, to form an N-oxide or sulfone.

The term "optionally substituted" refers to the presence or lack thereof of a substituent on the group being defined. When substitution is present the group may be mono-, di- or tri-substituted, independently, with alkyl, lower-alkyl, cycloalkyl, hydroxylower-alkyl, aminolower-alkyl, hydroxyl, thiol, amino, halo, nitro, lower-alkylthio, lower-alkoxy, mono-lower-alkylamino, di-lower-alkylamino, acyl, hydroxycarbonyl, lower-alkoxycarbonyl, hydroxysulfonyl, lower-alkoxysulfonyl, lower-alkylsulfonyl, lower-alkylsulfinyl, trifluoromethyl, cyano, tetrazoyl, carbamoyl, lower-alkylcarbamoyl, and di-lower-alkylcarbamoyl. Typically, electron-donating substituents such as alkyl, lower-alkyl, cycloalkyl, hydroxylower-alkyl, aminolower-alkyl, hydroxyl, thiol, amino, halo, lower-alkylthio, lower-alkoxy, mono-lower-alkylamino and di-lower-alkylamino are preferred.

The term "electron donating group" refers to a radical group that has a lesser affinity for electrons than a hydrogen atom would if it occupied the same position in the molecule. For example, typical electron donating groups are hydroxy, alkoxy (e.g. methoxy), amino, alkylamino and dialkylamino.

The term "leaving group" means a group capable of being displaced by a nucleophile in a chemical reaction, for example halo, nitrophenoxy, pentafluorophenoxy, alkyl sulfonates (e.g., methanesulfonate), aryl sulfonates, phosphates, sulfonic acid, sulfonic acid salts, and the like.

"Activating group" refers to those groups which, when attached to a particular functional group or reactive site, render that site more reactive toward covalent bond formation with a second functional group or reactive site. For example, the group of activating groups which can be used in the place of a hydroxyl group include --O(CO)Cl; --OCH₂ Cl; --O(CO)OAr, where Ar is an aromatic group, preferably, a p-nitrophenyl group; --O(CO) (ONHS); and the like. The group of activating groups which are useful for a carboxylic acid include simple ester groups and anhydrides. The ester groups include alkyl, aryl and alkenyl esters and in particular such groups as 4-nitrophenyl, N-hydroxylsuccinimide and pentafluorophenol. Other activating groups are known to those of skill in the art.

"Chemical library" or "array" is an intentionally created collection of differing molecules which can be prepared either synthetically or biosynthetically and screened for biological activity in a variety of different formats (e.g., libraries of soluble molecules; and libraries of compounds tethered to resin beads, silica chips, or other solid supports). The term is also intended to refer to an intentionally created collection of stereoisomers.

"Predefined region" refers to a localized area on a solid support which is, was, or is intended to be used for formation of a selected molecule and is otherwise referred to herein in the alternative as a "selected" region. The predefined region may have any convenient shape, e.g., circular, rectangular, elliptical, wedge-shaped, etc. For the sake of brevity herein, "predefined regions" are sometimes referred to simply as "regions." In some embodiments, a predefined region and, therefore, the area upon which each distinct compound is synthesized smaller than about 1 cm² or less than 1 mm². Within these regions, the molecule synthesized therein is preferably synthesized in a substantially pure form. In additional embodiments, a predefined region can be achieved by physically separating the regions (i.e., beads, resins, gels, etc.) into wells, trays, etc.

"Solid support", "support", and "substrate" refer to a material or group of materials having a rigid or semi-rigid surface or surfaces. In many embodiments, at least one surface of the solid support will be substantially flat, although in some embodiments it may be desirable to physically separate synthesis regions for different compounds with, for example, wells, raised regions, pins, etched trenches, or the like. According to other embodiments, the solid support(s) will take the form of beads, resins, gels, microspheres, or other geometric configurations.

Isolation and purification of the compounds and intermediates described herein can be effected, if desired, by any suitable separation or purification procedure such as, for example, filtration, extraction, crystallization, column chromatography, thin-layer chromatography, thick-layer (preparative) chromatography, distillation, or a combination of these procedures. Specific illustrations of suitable separation and isolation procedures can be had by references to the examples hereinbelow. However, other equivalent separation or isolation procedures can, or course, also be used.

A "channel block" is a material having a plurality of grooves or recessed regions on a surface thereof. The grooves or recessed regions may take on a variety of geometric configurations, including but not limited to stripes, circles, serpentine paths, or the like. Channel blocks may be prepared in a variety of manners, including etching silicon blocks, molding or pressing polymers, etc.

This invention provides novel compounds which are useful as linking groups in chemical synthesis, preferably in the solid phase synthesis of oligonucleotides and polypeptides and high density arrays thereof. These compounds are generally photolabile and comprise protecting groups which can be removed by photolysis to unmask a reactive group. The protecting group has the general formula Ar--C(R₁)(R₂)--O--C(O)--, wherein:

Ar is an optionally substituted fused polycyclic aryl or heteroaromatic group or a vinylogous derivative thereof;

R₁ and R₂ are independently H, optionally substituted alkyl, alkenyl or alkynyl, optionally substituted aryl or optionally substituted heteroaromatic, or a vinylogous derivative of the foregoing; and

X is a leaving group, a chemical fragment linked to Ar--C(R₁)(R₂)--O--C(O)-- via a heteroatom, or a solid support; provided that when Ar is 1-pyrenyl and R₁ =R₂ =H, X is not linked to Ar--C(R₁)(R₂)--O--C(O)-- via a nitrogen atom.

Preferred embodiments are those in which Ar is a fused polycyclic aromatic hydrocarbon and in which the substituents on Ar, R₁ and R₂ are electron donating groups. Particularly preferred protecting groups are the "PYMOC" protecting group, 1-pyrenylmethyloxycarbonyl, where Ar=1-pyrenyl and R₁ =R₂ =H, and the "ANMOC" protecting group, anthracenylmethyloxycarbonyl, where Ar =anthracenyl (e.g. 9-anthracenyl) and R₁ =R₂ =H.

Representative fused polycyclic aromatic hydrocarbons include naphthalene, phenanthrene, anthracene, benzoanthracene, dibenzoanthracene, heptalene, acenaphthalene, acephenanthrene, triphenylene, pyrene, fluorene, phenalene, naphthacene, picene, perylene, pentaphenylene, pyranthrene, fullerenes (including C₆₀ and C₇₀), and the like. A representative vinylogously substituted derivative of an aromatic hydrocarbon is styrene.

The invention also provides reagents of the molecular formula Ar--C(R₁)(R₂)--O--C(O)--X, where Ar, R₁, and R₂ have the meanings ascribed above, for incorporating the protecting group into the molecule desired to be protected. X can be any suitable leaving group such as halo, oxycarbonyl, imidazolyl, pentafluorophenoxy and the like, which is capable of reacting with a nucleophilic group such as hydroxy, amino, alkylamino, thio and the like on the molecule being protected. Thus, the reagents comprising the protecting groups disclosed herein can be used in numerous applications where protection of a reactive nucleophilic group is required. Such applications include, but are not limited to polypeptide synthesis, both solid phase and solution phase, oligo--and polysaccharide synthesis, polynucleotide synthesis, protection of nucleophilic groups in organic syntheses of potential drugs, etc.

The invention also provides compositions of the molecular formula Ar--C(R₁)(R₂)--O--C(O)--M, where Ar, R₁ and R₂ have the meaning outlined above and M is any other chemical fragment. Preferably, M will be a monomeric building block that can be used to make a macromolecule. Such building blocks include amino acids, nucleic acids, nucleotides, nucleosides, monosaccharides and the like. Preferred nucleosides are deoxyadenosine, deoxycytidine, thymidine and deoxyguanosine as well as oligonucleotides incorporating such nucleosides. Preferably, the building block is linked to the photolabile protecting group via a hydroxy or amine group. When nucleotide and oligonucleotide compositions are used, with the protecting groups of this invention, the protecting groups are preferably incorporated into the 3'--OH or the 5'--OH of the nucleoside. Other preferred compounds are protected peptides, proteins, oligonucleotides and oligodeoxynucleotides. Small organic molecules, proteins, hormones, antibodies and other such species having nucleophilic reactive groups can be protected using the protecting groups disclosed herein.

The use of nucleoside and nucleotide analogs is also contemplated by this invention to provide oligonucleotide or oligonucleoside analogs bearing the protecting groups disclosed herein. Thus the terms nucleoside, nucleotide, deoxynucleoside and deoxynucleotide generally include analogs such as those described herein. These analogs are those molecules having some structural features in common with a naturally occurring nucleoside or nucleotide such that when incorporated into an oligonucleotide or oligonucleoside sequence, they allow hybridization with a naturally occurring oligonucleotide sequence in solution. Typically, these analogs are derived from naturally occurring nucleosides and nucleotides by replacing and/or modifying the base, the ribose or the phosphodiester moiety. The changes can be tailor made to stabilize or destabilize hybrid formation or enhance the specificity of hybridization with a complementary nucleic acid sequence as desired.

Analogs also include protected and/or modified monomers as are conventionally used in oligonucleotide synthesis. As one of skill in the art is well aware oligonucleotide synthesis uses a variety of base-protected deoxynucleoside derivatives in which one or more of the nitrogens of the purine and pyrimidine moiety are protected by groups such as dimethoxytrityl, benzyl, tert-butyl, isobutyl and the like. Specific monomeric building blocks which are encompassed by this invention include base protected deoxynucleoside H-phosphonates and deoxynucleoside phosphoramidites.

For instance, structural groups are optionally added to the ribose or base of a nucleoside for incorporation into an oligonucleotide, such as a methyl, propyl or allyl group at the 2'--O position on the ribose, or a fluoro group which substitutes for the 2'--O group, or a bromo group on the ribonucleoside base. 2'--O--methyloligoribonucleotides (2'--O--MeORNs) have a higher afinity for complementary nucleic acids (especially RNA) than their unmodified counterparts. 2'--O--MeORNA phosphoramidite monomers are available commercially, e.g., from Chem Genes Corp. or Glen Research, Inc. Alternatively, deazapurines and deazapyrimidines in which one or more N atoms of the purine or pyrimidine heterocyclic ring are replaced by C atoms can also be used.

The phosphodiester linkage, or "sugar-phosphate backbone" of the oligonucleotide analogue can also be substituted or modified, for instance with methyl phosphonates or O--methyl phosphates. Another example of an oligonucleotide analogue for purposes of this disclosure includes "peptide nucleic acids" in which a polyamide backbone is attached to oligonucleotide bases, or modified oligonucleotide bases. Peptide nucleic acids which comprise a polyamide backbone and the bases found in naturally occurring nucleosides are commercially available from, e.g., Biosearch, Inc. (Bedford, Mass.).

Nucleotides with modified bases can also be used in this invention. Some examples of base modifications include 2-aminoadenine, 5-methylcytosine, 5-(propyn-1-yl)cytosine, 5-(propyn-1-yl)uracil, 5-bromouracil, and 5-bromocytosine which can be incorporated into oligonucleotides in order to increase binding affinity for complementary nucleic acids. Groups can also be linked to various positions on the nucleoside sugar ring or on the purine or pyrimidine rings which may stabilize the duplex by electrostatic interactions with the negatively charged phosphate backbone, or through hydrogen bonding interactions in the major and minor groves. For example, adenosine and guanosine nucleotides can be substituted at the N² position with an imidazolyl propyl group, increasing duplex stability. Universal base analogues such as 3-nitropyrrole and 5-nitroindole can also be included.

Compounds of this invention can be prepared by carbonylating an aromatic carbinol of the general formula Ar--C(R₁)(R₂)--OH with a carbonylation reagent such as for example, phosgene (COCl₂), carbonyldiimidazole or pentafluorophenoxy chloroformate and the like to provide Ar--C(R₁)(R₂)--O--C(O)--X where X is a leaving group derived from the carbonylating reagent (Cl, if phosgene was used, pentafluorophenoxy, if pentafluorophenoxy chloroformate was used, etc.). This intermediate, Ar--C(R₁)(R₂)--O--C(O)--X is then reacted with a molecule M carrying a nucleophilic group whose protection is desired to yield a protected building block Ar--C(R₁)(R₂)--O--C(O)--M. Representative aromatic carbinols are pyrenemethanol, naphthalenemethanol, anthracenemethanol, perylenemethanol and the like. Such aromatic carbinols are available from commercial suppliers such as Aldrich Chemical Co., Milwuakee, Wis. Alternatively, they may also be obtained from precursor aromatic hydrocarbons by acylation under Friedel-Crafts conditions with acid chlorides and anhydrides and subsequent reduction of the carbonyl group thus added to a carbinol.

Alternatively, one may first carbonylate the group on the molecule being protected with a carbonylation reagent, such as one described above, and subsequently displace the leaving group X thus inserted with the hydroxyl group of the aromatic carbinol. In either procedure, one frequently uses a base such as triethylamine or diisopropylethylamine and the like to facilitate the displacement of the leaving group.

One of skill in the art will recognize that the protecting groups disclosed herein can also be attached to species not traditionally considered as "molecules". Therefore, compositions such as solid surfaces (e.g., paper, nitrocellulose, glass, polystyrene, silicon, modified silicon, GaAs, silica and the like), gels (e.g., agarose, sepharose, polyacrylamide and the like to which the protecting groups disclosed herein are attached are also contemplated by this invention.

The protecting groups of this invention are typically removed by photolysis, i.e. by irradiation, though in selected cases it may be advantageous to use acid or base catalyzed cleavage conditions. Generally irradiation is at wavelengths greater than about 350 nm, preferably at about 365 nm. The photolysis is usually conducted in the presence of hydroxylic solvents, such as aqueous, alcoholic or mixed aqueous-alcoholic or mixed aqueous-organic solvent mixtures. Alcoholic solvents frequently used include methanol and ethanol. The photolysis medium may also include nucleophilic scavengers such as hydrogen peroxide. Photolysis is frequently conducted at neutral or basic pH.

This invention also provides a method of attaching a molecule with a reactive site to a support, comprising the steps of:

(a) providing a support with a reactive site;

(b) binding a molecule to the reactive site, said first molecule comprising a masked reactive site attached to a photolabile protecting group of the formula Ar--C(R₁)(R₂)--O--C(O)--, wherein:

Ar is an optionally substituted fused polycyclic aryl or heteroaromatic group or a vinylogously substituted derivative of the foregoing;

R₁ and R₂ are independently H, optionally substituted alkyl, alkenyl or alkynyl, or optionally substituted aryl or heteroaromatic group or a vinylogously substituted derivative of the foregoing; to produce a derivatized support having immobilized thereon the molecule attached to the photolabile protecting group; and

(c) removing the photolabile protecting group to provide a derivatized support comprising the molecule with an unmasked reactive site immobilized thereon.

As one of skill will recognize, the process can be repeated to generate a compound comprising a chain of component molecules attached to the solid support. In a "mix and match" approach, the photolabile protecting groups may be varied at different steps in the process depending on the ease of synthesis of the protected precursor molecule. Alternatively, photolabile protecting groups can be used in some steps of the synthesis and chemically labile (e.g. acid or base sensitive groups) can be used in other steps, depending for example on the availability of the component monomers, the sensitivity of the substrate and the like. This method can also be generalized to be used in preparing arrays of compounds, each compound being attached to a different and identifiable site on the support as is disclosed in U.S. Pat. Nos. 5,143,854, 5,384,261, 5,424,186 5,445,934 and U.S. patent application, Ser. No. 08/376,963, filed Jan. 23, 1995 (now abandoned), incorporated for reference for all purposes.

Thus, a related aspect of this invention provides a method of forming, from component molecules, a plurality of compounds on a support, each compound occupying a separate predefined region of the support, said method comprising the steps of:

(a) activating a region of the support;

(b) binding a molecule to the region, said molecule comprising a masked reactive site linked to a photolabile protecting group of the formula Ar--C(R₁)(R₂)--O--C(O)--, wherein:

Ar is an optionally substituted fused polycyclic aryl or heteroaromatic group or a vinylogously substituted derivative of the foregoing;

R₁ and R₂ are independently H, optionally substituted alkyl, alkenyl or alkynyl, or optionally substituted aryl or heteroaromatic group or a vinylogously substituted derivative of the foregoing;

(c) repeating steps (a) and (b) on other regions of the support whereby each of said other regions has bound thereto another molecule comprising a masked reactive site linked to the photolabile protecting group, wherein said another molecule may be the same or different from that used in step (b);

(d) removing the photolabile protecting group from one of the molecules bound to one of the regions of the support to provide a region bearing a molecule with an unmasked reactive site;

(e) binding an additional molecule to the molecule with an unmasked reactive site;

(f) repeating steps (d) and (e) on regions of the support until a desired plurality of compounds is formed from the component molecules, each compound occupying separate regions of the support.

A related method of forming a plurality of compounds on predefined regions of a support involves binding a molecule with a reactive site protected with a chemically labile protecting group to an activated region of the support and chemically removing the chemically labile protecting group to reveal the reactive site. The reactive site is then protected with a photolabile protecting group of this invention. This process is repeated for other regions of the support with other molecules as desired to provide a support having molecules with reactive sites protected by photolabile protecting groups on separate regions of the support. Reactive sites can be unmasked by removing the photolabile group from selected regions and coupled to additional molecules with photolabile protecting groups as described earlier to build up arrays of compounds on the support. Again, in a "mix and match" approach, monomers with chemically labile protecting groups can be attached to a reactive site on the substrate (i.e., on the support itself when the first layer of monomers is being assembled or subsequently onto an already attached monomer whose reactive site has been unmasked) and these chemically labile protecting groups can be replaced by a photolabile protecting groups of this invention. The replacement is accomplished by removing the chemically labile protecting group under conditions which do not affect any photolabile groups which may be on the support. This then reveals an unmasked reactive site on the monomer which had carried the chemically labile protecting group and this unmasked reactive site is reacted with a reagent of the formula Ar--C(R₁)(R₂)--O--C(O)--X, where X is a leaving group. Thereby, this region of the support is protected by a photolabile protecting group which can be selectively removed by light directed systems described in U.S. Pat. Nos. 5,143,854, 5,384,261, 5,424,186 and 5,445,934 and further described below. This method is particularly useful when the monomers are more readily available carrying chemically labile protecting groups than the photolabile protecting groups described herein. It will be recognized that any method of forming a chain of compounds or an array of compounds on a support using in at least one step a protecting group/reagent or compound of this invention is within the scope of the methods this invention.

Generally, these methods involve sequential addition of monomers to build up an array of polymeric species on a support by activating predefined regions of a substrate or solid support and then contacting the substrate with a protected monomer of this invention (e.g., a PYMOC protected nucleoside or amino acid). It will be recognized that the individual monomers can be varied from step to step. A common support is a glass or silica substrate as is used in semiconductor devices.

The predefined regions can be activated with a light source, typically shown through a screen such as a photolithographic mask similar to the techniques used in integrated circuit fabrication. Other regions of the support remain inactive because they are blocked by the mask from illumination and remain chemically protected. Thus, a light pattern defines which regions of the support react with a given monomer. The protected monomer reacts with the activated regions and is immobilized therein. The protecting group is removed by photolysis and washed off with unreacted monomer. By repeatedly activating different sets of predefined regions and contacting different monomer solutions with the substrate, a diverse array of polymers of known composition at defined regions of the substrate can be prepared. Arrays of 10⁶, 10⁷, 10⁸, 10⁹, 10¹⁰, 10¹¹, 10¹² or more different polymers can be assembled on the substrate. The regions may be 1 mm² or larger, typically 10 μm² and may be as small as 1 μm².

The methods described herein may also employ component molecules comprising a masked reactive site attached to a photolabile protecting group of the formula Ar--C(R₁)(R₂)--, wherein Ar, R₁, and R₂ have the meanings ascribed earlier. In such cases, the protecting group is attached to a reactive site that is not an amine and is removed by photolysis.

The solid substrate or solid support may be of any shape, although they preferably will be roughly spherical. The supports need not necessarily be homogenous in size, shape or composition, although the supports usually and preferably will be uniform. In some embodiments, supports that are very uniform in size may be particularly preferred. In another embodiment, two or more distinctly different populations of solid supports may be used for certain purposes.

Solid supports may consist of many materials, limited primarily by capacity for derivatization to attach any of a number of chemically reactive groups and compatibility with the synthetic chemistry used to produce the array and, in some embodiments, the methods used for tag attachment and/or synthesis. Suitable support materials typically will be the type of material commonly used in peptide and polymer synthesis and include glass, latex, polyethylene glycol, heavily cross-linked polystyrene or similar polymers, gold or other colloidal metal particles, and other materials known to those skilled in the art. The chemically reactive groups with which such solid supports may be derivatized are those commonly used for solid phase synthesis of the polymer and thus will be well known to those skilled in the art, i.e., carboxyls, amines, and hydroxyls.

To improve washing efficiencies, one can employ nonporous supports or other solid supports less porous than typical peptide synthesis supports; however, for certain applications of the invention, quite porous beads, resins, or other supports work well and are often preferable. One such support is a resin in the form of beads. In general, the bead size is in the range of 1 nm to 100 μm, but a more massive solid support of up to 1 mm in size may sometimes be used. Particularly preferred resins include Sasrin resin (a polystyrene resin available from Bachem Bioscience, Switzerland); and TentaGel S AC, TentaGel PHB, or TentaGel S NH₂ resin (polystyrene-polyethylene glycol copolymer resins available from Rappe Polymere, Tubingen, Germany). Other preferred supports are commercially available and described by Novabiochem, La Jolla, Calif.

In other embodiments, the solid substrate is flat, or alternatively, may take on alternative surface configurations. For example, the solid substrate may contain raised or depressed regions on which synthesis takes place. In some embodiments, the solid substrate will be chosen to provide appropriate light-absorbing characteristics. For example, the substrate may be a polymerized Langmuir Blodgett film, functionalized glass, Si, Ge, GaAs, GaP, SiO₂, SiN₄, modified silicon, or any one of a variety of gels or polymers such as (poly)tetrafluorethylene, (poly)vinylidendifluoride, polystyrene, polycarbonate, or combinations thereof. Other suitable solid substrate material will be readily apparent to those of skill in the art. Preferably, the surface of the solid substrate will contain reactive groups, which could be carboxyl, amino, hydroxyl, thiol, or the like. More preferably, the surface will be optically transparent and will have surface Si--OH functionalities, such as are found on silica surfaces.

The photolabile protecting groups and protected monomers disclosed herein can also be used in bead based methods of immobilization of arrays of molecules on solid supports.

A general approach for bead based synthesis is described in application Ser. Nos. 07/762,522 (filed Sep. 18, 1991, abandoned in favor of continuation-in-part application Ser. No. 07/946,239, which was abandoned in favor of continuation-in-part application Ser. No. 08/146,886, which issued as U.S. Pat. No. 5,639,603); 07/946,239 (filed Sep. 16, 1992, abandoned in favor of continuation-in-part application Ser. No. 08/146,886, which issued as U.S. Pat. No. 5,639,603); 08/146,886 (filed Nov. 2, 1993, now issued as U.S. Pat. No. 5,639,603); 07/876,792 (filed Apr. 29, 1992, now issued as U.S. Pat. No. 5,541,061) and PCT/US93/04145 (filed Apr. 28, 1993), Lam et al. (1991) Nature 354:82-84; PCT application no. 92/00091 and Houghten et al, (1991) Nature 354:84-86, each of which is incorporated herein by reference for all purposes.

Other methods of immobilization of arrays of molecules in which the photocleavable protecting groups of this invention can be used include pin based arrays and flow channel and spotting methods.

Photocleavable arrays also can be prepared using the pin approach developed by Geysen et al. for combinatorial solid-phase peptide synthesis. A description of this method is offered by Geysen et al., J. Immunol. Meth. (1987) 102:259-274, incorporated herein by reference.

Additional methods applicable to library synthesis on a single substrate are described in applications Ser. Nos. 07/980,523, filed Nov. 20, 1992 (now issued as U.S. Pat. No. 5,677,195), and 07/796,243, filed Nov. 22, 1991 (now issued as U.S. Pat. No. 5,384,261), incorporated herein by reference for all purposes. In the methods disclosed in these applications, reagents are delivered to the substrate by either (1) flowing within a channel defined on predefined regions or (2) "spotting" on predefined regions. However, other approaches, as well as combinations of spotting and flowing, may be employed. In each instance, certain activated regions of the substrate are mechanically separated from other regions when the monomer solutions are delivered to the various reaction sites. Photocleavable linkers are particularly suitable for this technology as this delivery method may otherwise result in poor synthesis fidelity due to spreading, reagent dilution, inaccurate delivery, and the like. By using a photocleavable linker, rather than a conventional acid-cleavable linker, the purest material can be selectively cleaved from the surface for subsequent assaying or other procedures. More specifically, masks can be used when cleaving the linker to ensure that only linker in the center of the delivery area (i.e., the area where reagent delivery is most consistent and reproducible) is cleaved. Accordingly, the material thus selectively cleaved will be of higher purity than if the material were taken from the entire surface.

Typically, the molecules used in this method will be the monomeric components of complex macromolecules. These monomeric components can be small ligand molecules, amino acids, nucleic acids, nucleotides, nucleosides, monosaccharides and the like, thereby allowing one to synthesize arrays of complex macromolecules or polymeric sequences, such as polypeptides, nucleic acids and synthetic receptors, on the solid support.

This invention discloses new nucleoside phosphoramidite monomers with 1-pyrenylmethyloxy-carbonyl ("PYMOC") 5'-protecting groups. They are photolytically cleaved under irradiation at wavelengths greater than about 350 nm, preferably at about 365 nm, in the presence of methanol, water, or water-solvent mixtures and/or with nucleophilic scavengers such as hydrogen peroxide at neutral or basic pH. The rate of photolysis is similar to that observed for the MeNPOC group. However, the yield of PYMOC photo-removal is much higher (˜95%), so that the use of these monomers for photochemical synthesis of oligonucleotides leads to higher stepwise cycle yields and therefore higher-purity oligomers.

The 1-pyrenylmethyloxycarbonyl group described here can be used for the protection of alcohols. The photolysis of PYMOC is faster than that of the 1-pyrenylmethyl group, so it would also be a superior photo-removable protecting group for phosphates, carboxylates, amines, thiols, etc.

Other "benzylic" oxycarbonyls may have similar or better efficiency than the PYMOC group. A general formula would be: ##STR1## where Ar is an optionally substituted fused polycyclic aryl or an optionally substituted heteroaromatic group or a vinylogously substituted derivative of the foregoing;

R₁ and R₂ are independently H, optionally substituted alkyl, alkenyl or alkynyl, optionally substituted aryl, optionally substituted heteroaromatic, or vinylogously substituted derivatives of the foregoing. Preferred embodiments are those in which Ar is a fused polycyclic aromatic hydrocarbon. FIG. 2 shows representative examples. Preferred substituents on the aromatic hydrocarbons would be electron-donating groups that stabilize an incipient excited state benzyl carbocation.

Other embodiments of the PYMOC photogroup, for example, include at least one additional substituent at the a position, such as a methyl group or a methoxy-substituted phenyl. These substituents will increase photosolvolysis efficiency, and improve the selectivity for the 5'-hydroxyl in the preparation of the monomer 5'-protected nucleoside.

EXAMPLE SYNTHESIS OF 5'--O--PYMOC-2'-DEOXYNUCLEOSIDE-3'--O--(N,N-DIISOPROPYL)CYANOETHYLPHOSPHORAMIDITES

All chemical reagents used were procured from commercial sources (Aldrich Chemical Co., Milwaukee, Wis. and Sigma Chemical Co., Milawaukee, Wis.). Intermediates and products were identified by mass spectrometry, ¹ H-NMR, and ³¹ P-NMR.

Abbreviations:

DIEA--Diethyl isopropylamine

NHS--N-hydroxysuccinimide

THF--Tetrahydrofuran

MeNPOC--methylnitropiperonyloxycarbonyl

TEA--Triethylamine

DMAP--4-Dimethylaminopyridine

Pentafluorophenyl Chloroformate

Pentafluorophenol (30 g; 163 mmol) and triethylamine (20 g, 200 mmol) were combined in 200 ml dry THF, and then added dropwise to a stirring solution of phosgene (20 g; 200 mmol) in 100 ml of toluene at 0° C. After 2 hours, the solution was filtered and evaporated to give the crude product as an oil, which was recrystallized from hexane to obtain 30 g (75%) pure pentafluorophenyl chloroformate.

5'--O--(1-Pyrenylmethyl)oxycarbonyl-2'-deoxynucleosides

The following general procedure was used to prepare 5'-PYMOC-derivatives of thymidine, N-4-isobutyryl-2'-deoxycytidine, N-7-phenoxyacetyl-2'-deoxyadenosine, and N-4-isobutyryl-2'-deoxyguanosine:

The base-protected nucleoside (20 mmol) was dried by co-evaporating 3 times with 50 ml dry pyridine, then dissolved in 20 ml CH₂ Cl₂ and 10 ml dimethylsulfoxide (DMSO) containing 1.7 ml (21 mmol) pyridine. The resulting solution was cooled to -10° C. under argon, and 5 g (20 mmol) of pentafluorophenyl chloroformate was added all at once with stirring. After an additional 2-3 hours stirring at -10° C., the reaction mixture was analyzed by TLC or HPLC to determine the extent of conversion. Additional quantities of pentafluorophenyl chloroformate and pyridine (˜0.4-1.0 mmol each) were then added, as needed, until the nucleoside was completely converted to the 5'--O--pentafluorophenoxycarbonyl derivative. Although isolable, at this point the intermediate was usually converted directly to the PYMOC-derivative, in situ, by the addition of 1-pyrenemethanol (6 g, 26 mmol), followed by 10 ml of triethylamine and 0.25 g (2 mmol) of N,N-dimethyl-aminopyridine, and stirring overnight at room temperature. About 50-100 ml of CH₂ Cl₂ was then added, and in the case of thymidine, the pure PYMOC-derivative precipitated and could be collected by filtration. Otherwise, the solution was washed twice with 5% aqueous NaHCO₃, once with saturated NaCl, dried with Na₂ SO₄, and evaporated to dryness. The crude material was finally purified by flash chromatography (silica gel, 2:8 ethyl acetate-CH₂ Cl₂ /1-6% methanol gradient) to obtain the pure 5'-PYMOC nucleoside products in ˜75% yield.

5'--O--(1-Pyrenylmethyl)oxycarbonyl-2'-deoxynucleoside-3'--O--(N,N-diisopropyl)cyanoethylphosphoramidites

On a 12 mmol scale, the 5'-PYMOC nucleosides were first dried by co-evaporation with dry pyridine, and then dissolved or suspended in 50 ml of dry CH₂ Cl₂. Then 2-cyanoethyl-N,N,N¹,N¹ -tetraisopropylphosphorodiamidite (4.4 g; 14.5 mmol) and N,N-diisopropylammonium tetrazolide (1 g; 6 mmol) were added, and the mixture was left stirring under argon overnight. The solution was washed twice with 10% aqueous NaHCO₃, once with saturated NaCl, dried with Na₂ SO₄, and then evaporated to dryness. The crude products were purified by flash chromatography (silica gel, eluting with a 1-5% methanol gradient in 2:8 ethyl acetate-CH₂ Cl₂ containing 0.5% triethylamine) to obtain the pure phosphoramidites in ˜80% yield.

Table 1 compares the efficiency of photolytic cleavage of PYMOC protected nucleosides to MeNPOC (methylnitropiperonyloxycarbonyl) protected nucleosides.

                  TABLE 1                                                          ______________________________________                                         Photolysis Rates:                                                                        5'-Protecting                                                                                                 Base Group Solvent Power                                                      .sub.1/2                               ______________________________________                                         T     MeNPOC     dioxane      35 mW/cm.sup.2                                                                          9 sec                                     T PYMOC MeOH " 10 sec                                                          T PYMOC 1:1 dioxane-H.sub.2 O " 10 sec                                         T PYMOC 9:1 dioxane-MeOH " 43 sec                                              G.sup.ibu MeNPOC dioxane 27 mW/cm.sup.2 11 sec                                 G.sup.ibu PYMOC MeOH " 13 sec                                                ______________________________________                                    

Table 2 compares the coupling cycle efficiency (six cycles) of PYMOC protected and MeNPOC protected nucleosides to a phosphoramidite solid support using surface fluorescence analysis.

                  TABLE 2                                                          ______________________________________                                         Stepwise Coupling Cycle Efficiencies:                                            1. Surface fluorescence analysis ("staircase" assay):                                      5'-Protecting                                                                              Yield (6 steps)                                      Base      Group       Net    Avg. Stepwise                                     ______________________________________                                         T         MeNPOC      15     73                                                  T PYMOC 56 91                                                                  dG.sup.ibu MeNPOC 29 81                                                        dG.sup.ibu PYMOC 61 92                                                         dC.sup.ibu MeNPOC 37 85                                                        dC.sup.ibu PYMOC 68 94                                                       ______________________________________                                    

Table 3 compares the coupling cycle efficiency (six cycles) of PYMOC protected and MeNPOC protected nucleosides to a phosphoramidite solid support using HPLC analysis.

                  TABLE 3                                                          ______________________________________                                         2. HPLC analysis (DOP#AF001; 3" ethenodeoxyadenosine tag):                                   5'-Protecting                                                                              Yield (3 steps)                                      Base      Group     Net        Avg. Stepwise                                   ______________________________________                                         T         PYMOC     92         97.2                                              T "  93 97.6 avg 97.4                                                          T MeNPOC 45 77                                                                 T " 43 75                                                                      T " 48 78                                                                      T " 40 74                                                                      T " 48 78 avg 76.4                                                           ______________________________________                                    

The foregoing invention has been described in some detail by way of illustration and example, for purposes of clarity and understanding. It will be obvious to one of skill in the art that changes and modifications may be practiced within the scope of the appended claims. Therefore, it is to be understood that the above description is intended to be illustrative and not restrictive. The scope of the invention should, therefore, be determined not with reference to the above description, but should instead be determined with reference to the following appended claims, along with the full scope of equivalents to which such claims are entitled.

All patents, patent applications and publications cited in this application are hereby incorporated by reference in their entirety for all purposes to the same extent as if each individual patent, patent application or publication were so individually denoted. 

What is claimed is:
 1. A method of attaching a molecule with a reactive site to a support comprising the steps of:(a) providing a support with a reactive site; (b) binding a molecule to the reactive site, said first molecule comprising a masked reactive site attached to a photolabile protecting group of the formula Ar--C(R₁)(R₂)--O--C(O)--, wherein: Ar is an optionally substituted fused polycyclic aryl or heteroaromatic group or a vinylogously substituted derivative of the foregoing; R₁ and R₂ are independently H, optionally substituted alkyl, alkenyl or alkynyl, or optionally substituted aryl or heteroaromatic group or a vinylogously substituted derivative of the foregoing;to produce a derivatized support having immobilized thereon the molecule attached to the photolabile protecting group; and (c) removing the photolabile protecting group to provide a derivatized support comprising the molecule with an unmasked reactive site immobilized thereon.
 2. The method of claim 1, wherein the binding step in (b) forms a covalent linkage.
 3. The method of claim 2, further comprising:(a) coupling a second molecule to the unmasked reactive site, which second molecule comprises a second masked reactive site attached to the photolabile protecting group to produce a derivatized support having immobilized thereon a chain of the first and second molecules; and (b) removing the photolabile protecting group to provide a derivatized support with a chain of the first and second molecules with a second unmasked reactive site immobilized thereon.
 4. The method of claim 3, further comprising repeating steps (a) and (b) with a succession of molecules to provide a chain of molecules immobilized on the support.
 5. The method of claim 4, wherein the molecules are deoxynucleosides.
 6. The method of claim 5, wherein the support is a glass or silica substrate.
 7. The method of claim 1, wherein Ar is independently 1-pyrenyl or 9-anthracenyl, R₁ =H and R₂ is independently H, methyl, p-methoxyphenyl, 3,5-dimethoxyphenyl, 9-anthracenyl or 1-pyrenyl.
 8. The method of claim 7, wherein Ar is 1-pyrenyl and R₁ and R₂ are H.
 9. The method of claim 5, wherein the deoxynucleosides are linked to the photolabile group via a 5'--OH.
 10. The method of claim 1, wherein the photolabile group is removed by irradiation at a wavelength of greater than 350 nm.
 11. The method of claim 10, wherein the wavelength is about 365 nm.
 12. A method of forming, from component molecules, a plurality of compounds on a support, each compound occupying a separate predefined region of the support, said method comprising the steps of:(a) activating a region of the support; (b) binding a molecule to the first region, said molecule comprising a masked reactive site linked to a photolabile protecting group of the formula Ar--C(R₁)(R₂)--O--C(O)--, wherein: Ar is an optionally substituted fused polycyclic aryl or heteroaromatic group or a vinylogously substituted derivative of the foregoing; R₁ and R₂ are independently H, optionally substituted alkyl, alkenyl or alkynyl, or optionally substituted aryl or heteroaromatic group or a vinylogously substituted derivative of the foregoing; (c) repeating steps (a) and (b) on other regions of the support whereby each of said other regions has bound thereto another molecule comprising a masked reactive site linked to the photolabile protecting group, wherein said another molecules may be the same or different from that used in step (b); (d) removing the photolabile protecting group from one of the molecules bound to one of the regions of the support to provide a region bearing a molecule with an unmasked reactive site; (e) binding an additional molecule to the molecule with an unmasked reactive site; (f) repeating steps (d) and (e) on regions of the support until a desired plurality of compounds is formed from the component molecules, each compound occupying separate regions of the support.
 13. The method of claim 12, wherein the binding steps form covalent linkages.
 14. The method of claim 13, wherein the molecules are deoxynucleosides.
 15. The method of claim 14, wherein the support is a glass or silica substrate.
 16. Th e method of claim 12, wherein Ar is independently 1-pyrenyl or 9-anthracenyl, R₁ =H and R₂ is independently H, methyl, p-methoxyphenyl, 3,5-dimethoxyphenyl, 9-anthracenyl or 1-pyrenyl.
 17. The method of claim 16, wherein Ar is 1-pyrenyl and R₁ and R₂ are H.
 18. The method of claim 14, wherein the deoxynucleosides are linked to the photolabile group via a 5'--OH.
 19. The method of claim 12, wherein the photolabile group is removed by irradiation at a wavelength of greater than 350 nm.
 20. The method of claim 19, wherein the wavelength is about 365 nm.
 21. The method of claim 14, wherein at least 106 chains a re immobilized on the support.
 22. The method of claim 12, wherein each of the regions has an area of between about 1 μm² and 10,000 μm².
 23. The method of claim 12, further comprising:(g) covalently binding a second molecule comprising a masked reactive site linked to a chemically labile protecting group to a reactive site, wherein the reactive site is either on an activated region of the support as formed in step (a) or is an unmasked reactive site on a molecule on the support as formed in step (d); (h) replacing the chemically labile protecting group with the photolabile protecting group to provide a region of the support having a molecule with the photolabile protecting group; and (i) repeating steps (d)-(f) of claim as desired.
 24. A method of attaching a molecule with a reactive site to a support comprising the steps of:(a) providing a support with a reactive site; (b) binding a molecule to the reactive site, said molecule comprising a masked reactive site attached to a photolabile protecting group of the formula Ar--C(R₁)(R₂)--, wherein: Ar is an optionally substituted fused polycyclic aryl or heteroaromatic group or a vinylogously substituted derivative of the foregoing; R₁ and R₂ are independently H, optionally substituted alkyl, alkenyl or alkynyl, or optionally substituted aryl or heteroaromatic group or a vinylogously substituted derivative of the foregoing; to produce a derivatized support having immobilized thereon the molecule attached to the photolabile protecting group; and (c) removing, by irradiation, the photolabile protecting group to provide a derivatized support comprising the molecule with an unmasked reactive site immobilized thereon.
 25. A method of forming, from component molecules, a plurality of compounds on a support, each compound occupying a separate predefined region of the support, said method comprising the steps of:(a) activating a region of the support; (b) binding a molecule to the first region, said molecule comprising a masked reactive site linked to a photolabile protecting group of the formula Ar--C(R₁)(R₂)--, wherein: Ar is an optionally substituted fused polycyclic aryl or heteroaromatic group or a vinylogously substituted derivative of the foregoing; R₁ and R₂ are independently H, optionally substituted alkyl, alkenyl or alkynyl, or optionally substituted aryl or heteroaromatic group or a vinylogously substituted derivative of the foregoing; (c) repeating steps (a) and (b) on other regions of the support whereby each of said other regions has bound thereto another molecule comprising a masked reactive site linked to the photolabile protecting group, wherein said another molecules may be the same or different from that used in step (b); (d) removing, by irradiation, the photolabile protecting group from one of the molecules bound to one of the regions of the support to provide a region bearing a molecule with an unmasked reactive site; (e) binding an additional molecule to the molecule with an unmasked reactive site; (f) repeating steps (d) and (e) on regions of the support until a desired plurality of compounds is formed from the component molecules, each compound occupying separate regions of the support.
 26. A method of attaching to a solid support a molecule with a masked reactive site linked to a photolabile protecting group having a formula Ar--C(R₁)(R₂)--O--C(O)--, wherein:Ar is an optionally substituted fused polycyclic aryl or heteroaromatic group or a vinylogously substituted derivative of the foregoing; and R₁ and R₂ are independently H, optionally substituted alkyl, alkenyl or alkynyl, or optionally substituted aryl or heteroaromatic group or a vinylogously substituted derivative of the foregoing; said method comprising the steps of: (a) activating a region of the support; (b) binding a molecule to the first region, said molecule comprising a masked reactive site linked to a protecting group; (c) removing the protecting group to provide a region bearing a molecule with an unmasked reactive site; (d) protecting the unmasked reactive site by exposing it to a reagent of the formula Ar--C(R₁)(R₂)--O--C(O)--X, wherein X is a leaving group, to provide a support with a molecule with a masked reactive site linked to a photolabile protecting group.
 27. A method of forming, from component molecules, a plurality of compounds on a support, each compound occupying a separate predefined region of the support, said method comprising the steps of:(a) activating a region of the support; (b) binding a molecule to the first region, said molecule comprising a masked reactive site linked to a protecting group; (c) repeating steps (a) and (b) on other regions of the support whereby each of said other regions has bound thereto another molecule comprising a masked reactive site linked to a protecting group, wherein said another molecules and protecting groups can be the same or different 12 to each other; (d) removing the protecting group from one of the molecules bound to one of the regions of the support to provide a region bearing a molecule with an unmasked reactive site; (e) binding an additional molecule to the molecule with an unmasked reactive site; (f) repeating steps (d) and (e) on regions of the support, until a desired plurality of compounds is formed from the component molecules, each compound occupying separate regions of the support, with the proviso that at least one of the protecting groups used in steps (a)-(f) is a photolabile protecting group of the formula Ar--C(R₁)(R₂)--O--C(O)--, wherein: Ar is an optionally substituted fused polycyclic aryl or heteroaromatic group or a vinylogously substituted derivative of the foregoing; R₁ and R₂ are independently H, optionally substituted alkyl, alkenyl or alkynyl, or optionally substituted aryl or heteroaromatic group or a vinylogously substituted derivative of the foregoing.
 28. The method of claim 27, wherein the binding steps from covalent linkages.
 29. The method of claim 23 wherein the binding steps form covalent linkages. 